The present invention is related generally to power control and, more particularly, to a system and method for power control in a wireless communication system.
Power control in a wireless communication system is desirable for many reasons. For example, battery power conservation in a wireless communication device is optimized by controlling the transmitter output power such that the device does not transmit with excessive power. In addition, lowering the transmission output power decreases the interference to other wireless communication devices.
In certain wireless communication systems, such as a code division multiple access (CDMA) communication system, power control is absolutely essential. As those skilled in the art can appreciate, CDMA technology assigns statistically uncorrelated binary sequences, sometimes referred to as pseudo-random sequences, to each wireless communication device. The data signal from a CDMA device is modulated in a pseudo-random fashion using the pseudo-random sequences such that a receiver can demodulate using the same pseudo-random sequence to recover the data signal while any other signals are decoded as noise. Thus, an increase in the power of signals will also increase the noise at any given device.
If one CDMA device increased its transmission power, the signal for that particular device would increase, but at the cost of a decreased signal-to-noise ratio (SNR) for every other user. That is, an increased signal for one user results in increased noise for every other user and vice versa. To offer this decrease in SNR, each of the other users will have to increase their signal power, which in turn will increase the noise level for all users. It is therefore easy to appreciate the importance of each user providing the correct amount of signal power required and no more. As a result, it is essential to transmit at the lowest possible power level that will still allow acceptable quality of communication. In addition, the channel usually changes with time and the received power can change rapidly thus requiring a dynamic power control mechanism.
Power control in a forward link of a CDMA system is particularly difficult during handoff. In a xe2x80x9csoftxe2x80x9d handoff, the wireless device may be communicating with two or more base transceiver subsystems (BTS). If power control is not adequately regulated, the BTSs can transmit at radically different powers resulting in an overall system imbalance. Therefore, it can be appreciated that there is a significant need for a system and method that controls power in a wireless communication system. The present invention provides this, and other advantages, as will be apparent from the following description and accompanying figures.
The present invention is embodied in a system and method for the control of transmitter power on the forward link of a wireless communication system. A wireless communication device transmits data to a plurality of base station transceiver subsystems (BTSs). The data transmitted from the wireless communication device includes power control data, which is subject to noise and interference. Each base station transceiver receives the power control data and adjusts the output transmission power of its transceiver in accordance with the power control data. In addition, each base station transceiver stores the power control data, or data related thereto, in a power control history storage area.
The system further includes a selector that receives data from both base station transceivers, and further receives the power control history data from each base station transceiver. The selector selects the best data from one of the base station transceivers for further processing by the communication system. In addition, the selector generates a reference power control history based on one or both of the received power control histories. The reference power control history data is used to adjust the transmitter output power of the transceivers in one or both of the base station transceivers.
In one embodiment, the selector utilizes the power control history from the base station transceiver whose frame was selected for further processing. Alternatively, the selector may combine the power control history data from both base station transceivers to generate the reference power control history.
The selector may transmit a single power control command to a base station transceiver to adjust the transmitter output power thereof. Alternatively, the selector may transmit a series of incremental commands to adjust the transmitter output power of the base station transceiver. In yet another alternative embodiment, the selector may transmit the reference power control history data to the base station transceiver to allow the base station to generate its own power control commands.